Ophthalmometer



Sept. 26, 1939.

H. HARTINGER 2,174,308

OPHTHALMOMETER Original Filed Jan. 1l, 1937 1,/ v Invenor:

Patented Sept. 26, '1939 UNITED STATES PATENT OFFICE l 2,114,308 oPn'rnArMoMn'rEa Hans Hartinger, Jena, Germany, assigner to the firm of Carl Zeiss.) Jena, Germany Original application January 11, 1937, Serial No. 119,970. Divided and this application April 3, 1939, Serial No. 265,817. In Germany. January `'implication-s have been filed in Germany, J anuary 27, 1936, and in Switzerland, January 7, 1937. In my copending United States application Ser. No. 119,'970, illed January 11, 1937, of which of the two test-mark images reflected by the.

l0 cornea and for adjusting these two double images relatively to each other.

The reciprocal adjustment of the two double images is achieved by means of the two interior of all `iour images, the two exterior images only 1B disturbing the measurement; Y

The invention provides linearly polarizing means, which are to eiect the disappearance of the said two exterior images. These-means are to produce an image of each test mark through 20 the agency of polarized light. It is advantageous to use to this effect two foils, for instance of herapathite, which polarize the light linearly and each oi.' which is coordinated to one of the two test marks, and which are so disposed that their planes of oscillation are at right angles to each other.

In contradistinction to the embodiments described in my said copending application, the reiiected images o! the two test marks are doubled so by doubly reiracting crlstals, for instance a Wollaston calcite prism. These cristals serve at the same time as analyzers; They and the said two foils (or, if other means are used for polarizing the light projecting the test marks on the 35 cornea, such other means) will cooperate, when suitably arranged, in such a manner that the intended disappearance of the two exterior images is effected without any additional'means being required.

l inthe accompanying drawing, which illustrates through the optical axis o! the objective a constructional example of anl ophthalmometer and `Figure 2 shows the double images produced. For

the sake of simplicity, the drawing does not show( those well-known parts oi the ophthalmometer duced double images, and the bright mark which is disposed in the observation device and to be t, viewed by the eye under examination.

the invention, Figure 1 represents in a section.

'1 (Cl. 88--21Dl In Figure 1, the optical observation device has an objective l iixed into a tubular housing 2 which is assumed to be rotatable about the axis X--X of the said objective. To the housing 2 are fixed two tubular bodies 3 and 4 whose axes Y-Y and ZZ, respectively, intersect each other at a point 5 corresponding approximately to the position which the centre of curvature of the cornea 6 oi an eye I` to be examined assumes relatively to the instrument. Into the tubular 10 bod?,v 3 is fixed a glass plate 8 bearing a test mark 9 illuminated by a source of light I0. Between the glass plate 8 -and another glass plate il is cemented a herapathite foil i2 which polarizes linearly the light emitted by the source of 1l light l0 and whose plane of oscillation is at right angles to the plane of the drawing. Into the tubular body I is fixed a glass plate I3 bearing a test mark Il illuminated by a source of light l5. Between the glass plate I3 and another glass 90 plate i8 is cemented a herapathite foil i'l which polarizes linearly the light emitted by the source of light I5 and whose plane of oscillation coincides with the plane of the drawing. The two images due to reflection of the two test marks g5 9 and I l on the cornea 6 are doubled by a Wollaston prism which consists of two calcite prisms I8 and I9 whose planes of oscillation are at right angles and parallel to the plane ot lthe drawing, respectively. cillation of the two foils and the planes of oscillation of the said calcite prisms Il and I9 assume the positions indicated above, the two exterior halves of the two double images of thetwo reiiectedtest-mark images are caused to disappear. 35 For the reciprocal adjustment of the two interior halves ofthe two double images, which remain visible, the Wollaston prism I8, Il is so mounted in the tube 2 as to be dlsplaceable along the axis X-X. The mount 2l of the prism-has o a pin 2l extending through a longitudinal aperture 22 ci the tube 2 and engaging in a helical groove 23' of a sleeve 2( which is rotatable relatively to the tubev 2. Displacements of the Wollaston prism I8, l2 along the axis X-X are effected by rotating the sleeve 24 relatively to the tube 2. The device which is to indicate the curvature of the cornea, and is omitted in the drawing, contains an index iixed to the sleeve 24 and a scale provided on the housing 2.

When using the instrument, the observer see--Y ing in the (omitted) eye-piece of the observation device the interior Vhalves of the two double 'images which the Wollaston prism ll, Il produces o! the reected test-mark isto dis- ,f

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